[NLRS] 10GHz feed horn design & question

[Al Bergman]

How many inches is that Jon?  (smile)...
Al

----- Original Message ----- 
From: <W0ZQ at aol.com>
To: <nlrs at mailman.qth.net>
Sent: Wednesday, November 24, 2004 11:29 AM
Subject: [NLRS] 10GHz feed horn design & question


> I finally measured the dimensions of my "larger" 10gigs offset dish
that I
> have been using this summer.   Here are the stats:
>
> Largest axis (top to bottom) = 654.05 mm
> Shortest axis (left to right) = 596.90 mm
> Deepest spot along largest axis = 58.42 mm
> Deepest spot from bottom along axis = 292.10 mm
>
> Using hdl_3b3, this dish, at 10368.1 has the following attributes:
> Focal length = 357.9 mm
> Full parabola f/D = 0.3
> Focal point is located 357.92 mm from bottom edge and 611.73 mm from
top  edge
> Large axis tilt (to get beam on the horizon) = 67.2 degrees
> Use a feedhorn design of f/D = 0.68
> With 50% efficiency, gain is 33.2 dBi
> With 60% efficiency, gain is 34.0 dBi
>
> So then I punched the f/D = 0.68 data into the horn design and
generated a
> template for an 11.29 dBi horn (at 10368).   The horn that  is
currently on
> this dish is a RCA DSS horn with a gain of 11.49  dBi.   When I hold
the two
> templates up against each other over a  strong light source to compare
them, they
> are indeed just a little bit  different.
>
> So, for the dish guru's out there, will changing the feedhorn from the
> current RCA DSS feed horn (11.49 dBi) to a more appropriate feedhorn
(11.29  dBi)
> provide better illumination for the slightly larger dish and hence a
bit  more
> gain ?   My thinking is yes, but the improvement may be on the  order
of one
> dB or so (its not the difference in the gain of the two  feedhorns
..... is it
> ?), certainly not a BIG deal, but a deal none the  less.
>
> 73,  Jon
> W0ZQ
>
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